A sealed type secondary battery that can be charged and discharged has a high energy density. Therefore, an abnormal charge/discharge reaction or chemical reaction occurs in the battery, resulting in generation of gas, when such a battery is used for a long time in high temperature environments, or when an internal or external short circuit occurs, or when abnormal heating, abnormal impact, or the like, occurs. Accordingly, a battery case may swell or even explode.
In order to solve such problems, Patent Literature 1 describes a sealed type battery including a safety valve in a sealing member. According to PTL 1, the safety valve in the sealing member breaks due to a rapid increase in the pressure in the battery, and gas in the battery is exhausted through a gas exhaust hole in a battery lid to the outside of the battery. Thus, the battery case can be prevented from swelling and exploding.